Analysis of a trampled formation: Brown Leucitic Tuff (Roccamonfina volcano)
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Santello Lisa
Dipartimento di Geoscienze, Università degli studi di Padova
Few years ago several human
footprints (about 100) were
found over a very steep volcanic surface of the Roccamonfina volcanic area (CE)
n
ITALY
ROME
OPEN QUESTIONS
1. Where were impressed the footprints?
2. Why was possible the preservation of the footprints?
3. How was possible the conservation of the footprints?
4. When the footprints were impressed?
5. Who made the footprints?
ROCCAMONFINA
VOLCANO
BROWN LEUCITIC TUFF (BLT)
GEOLOGICAL SETTING:
ROCCAMONFINA VOLCANO
3 main activity epochs
n
2 magmatic series
Galluccio
n
Mt. Cesima
Mt. Camino
Cave
Volpara
Conca Campania
Aurunci Mts.
Aurunci Mts.
n
Mt. Cesima
Mt. Camino
- BLT: the trampled formation;
- 385-325 ka;
- Result of explosive activity
of the second activity epoch
of Roccamonfina volcano;
- It crops out mainly from N
to SW sectors of the volcanic
area
- It can be subdivided into
several similar units;
- Locally it presents widespread lithification;
- Sub-Plinian eruption.
Brown Leucitic Tuff
Caldera rim
FORESTA
CARANGI
Campagnola
Mt. Maggiore
Mt. Maggiore
Roccamonfina
Mt. Massico
Mt. Massico
Ponte
Teano
2 km
2 km
Epoch I products
Quaternary sediments
Terrigenous and Carbonate sequences
Epoch II products
Terrigenous and Carbonate sequences
HK series products
Caldera rim
K series products
Epoch III products
Quaternary sediments
Cupa
Caldera rim
Roccamonfina volcano activity can be subdivided into three
main epochs: 1) stratovolcano building, 2) Explosive eruptions
series, 3) lava domes buildings.
Distribution of the BLT around Roccamonfina volcanic area
G
O
Its products can be ascribed to two
R
T
E
P
D
N
A
magmatic series: HK and
Y
H
P
A
R
G
I
K series.
T
A
R
BLT stratigraphy, with grain-size analyses
ST
The BLT
can be subdivided into 8 similar units.
35
Lithic Fragments
Pumices
Lithification
LS8’’
30
The grain-size of each unit unit is analysed
with statistical parameters.
Composition
tephriphonolite to phonotephrite, with wide
analicimization of the leucite
crystals and zeolitization
3 km
Y
H
P
RA
35
Sessa Aurunca
30
LS7’’
LITH
IFICA
TION
PRO
CESS
The process
: ZEO
LITIZ
permitting the impresATIO
N
sion and the conservation of the
footprints is the zeolitization. The zeolites (Chabazite and Phillipsite) nucleation creates a rigid framework among
the particles of the pyroclastic deposits,
leading to lithification.
Temperature range stability of Chabazite and
Phillipsite is from 100 °C to 20 °C
Chabazite
modified from Chipera & Apps, 2001
PREFACE: THE HUMAN FOOTPRINTS
Levyne
25
Stability fields for zeolites:
TEMPERATURE
GLASS CHEMISTRY
WATER CONTENT
LS6’’
Stratigraphic height (m)
LS6’
LS5’’
LS5’
Layer (LSn’’): expression of a pyroclastic flow
event.
Inside this layer 4 different members can be recognized, labeled α, β1, β2 and γ.
α bed = ground surge coming before the pyroclastic
flow.
level β1= fine-grained basal part of a pyroclastic
flow unit.
level β2 = main body of the pyroclastic flow.
level γ = very fine ash bed.
LS4’’
20
20
LS4’
15
LS3’
LS4
10
0
10
1.0
Lithification
200
(K+Na)/(K+Na+Ca)
5
1m
0
-3,00
tephra
-2,00
-1,00
LS8
0
0,00
MdΦ
flow
300
phillipsite
zite
chaba
0.6
0.4
heulandite
1,00
2,00
0,00
1,00
σΦ
2,00
clinoptilolite
1.0
3,00
1.0
1.5
2.0
2.5
3.0
Si/Al
1,0
LS2’’
2 km
2 km
n
LS7
1,0
1,0
2,0
3,0
FORESTA
2,0
3,0
FORESTA
FORESTA
CARANGI
CARANGI
A
CARANGI
Roccamonfina
2 km
2 km
n
LS8’’
100
200
300
400
500
Temperature (°C)
Height (m)
LS5
2 km
C
1,0
2,0
Conca Campania
FORESTA
1,0
0
Ponte
Ponte
Teano
Cupa
Sessa Aurunca
Sessa Aurunca
Sessa Aurunca
100
0
50
100
%
Distribution of the zeolitization along the stratigraphy. Phillipsite is stable at higher T and it is so present where the lithic
fragments are more aboundant and vice versa for Chabazite.
Footprints unit (LS7): 349 + - 3 ka
Following unit (LS8): 350 + - 3 ka
MIETTO P., AVANZINI M. & ROLANDI G. (2003)
SPARKS R. S. J. (1976)
SPARKS R. S. J., SELF S. & WALKER G. P. L. (1973)
100
200
300
400
500
Temperature (°C)
600
700
20 m deposit, 720 °C, emplaced on 1 m of water
1 mo
nth
10
8
6
s
th
Campagnola
Roccamonfina
Roccamonfina
50
%
3,0
Roccamonfina
r
on
2,0
CARANGI
CARANGI
CARANGI
0
700
1 year
3,0
1y
ea
7m
FORESTA
FORESTA
Cave
Height (m)
3,0
Volpara
nths
8
12
Galluccio
1,0
600
th
7 mo
4
n
2,0
ths
4
LS1
LS7’’
h
ont
8
0
LS6’’
on
on
12
r
Sessa Aurunca
7m
ea
1y
LS6
Rainfall; 20 cm/month; 20 m sheet, 675°C
1m
1m
Roccamonfina
Sessa Aurunca
5.0
16
12
CARANGI
B
No rainfall; 20 m sheet, 675°C
16
Campagnola
Roccamonfina
4.5
modified from Chipera & Apps, 2001
Height (m)
3,0
4.0
Meteoric precipitions appear to be the most favourable conditions for the nucleation of the zeolites
2 km
n
3.5
LS2
LS4’’
LS3’’
2,0
3,0
Roccamonfina
250
LS1’
FORESTA
References:
AVANZINI M., MIETTO P., PANARELLO A., DE ANGELIS M. & ROLANDI G. (2008)
DE RITA D. & GIORDANO G. (1996)
LUHR J. F. & GIANNETTI B. (1987)
analcime
0.2
1,0
Ar/Ar dating of the trampled surface
are important to establish who made
the footprints
150
Footprints
LS3
n
DATING
100
The composition of BLT glass shards is compatible
with the formation of Chabazite and Phillipsite
LS2’
Sessa Aurunca
Sessa Aurunca
50
0.8
2,0
Isopach maps of BLT flow
units, useful to understand
the migration of the vent
during the eruption
Laumontite
LS2’’
Roccamonfina
2 km
Phillipsite
Phillipsite
Pumices
CARANGI
n
Mordenite
K-chabazite
Lithic Fragments
n
Sessa Aurunca
Epistilbite
15
LS3’’
2,0
3,0 FORESTA
4,0
Stilbite
modified from Hall, 1998
2 km
Heulandite
Analcime
Wairakite
LS1’’
n
Mesolite/Scolecite
Stability temperature (°C)
5
This particular succession of sub-units is
repeated in all the units. As a matter of
fact the BLT cycle is composed by several
eruptive pulses with similar characterisLS1’’
tics.
Some of these units
are strongly lithified.
The human footprints
were impressed over
the last lithified unit
(LS7) and they were
LS5’’
covered by LS8 not
lithified unit.
Thomsonite
Gismondine
Zeolite mineral
Basal sub-unit (LSn’): alternation between
pumice-rich beds and ash-rich beds, evidence of
an instable sustained eruptive column.
25
4
2
0
100
200
300
400
500
Temperature (°C)
600
700
800
late archaic
Completely
indistiguishable
Homo heidelbergensis
Neandertals
modern humans
Homo sapiens
Homo erectus
800
700
600
500
400
ka
300
200
100
0
Acnowledgements
I thank Prof. H. U. Schmincke and Prof. R. S. J. Sparks for critical comments and precious suggestions.
This work was supported by IAS and Borsa di studio per l’estero Fond. “Ing. Aldo Gini”